Mutagenicity and chemical characterization of organic constituents in rice straw smoke particulate matter

Pesticides and Related Toxicants in the Atmosphere

Pesticides and other toxicants released into the environment can contaminate air, water, soil, and biota. This review focuses on sources, exposures, fate, analysis, and trends. The potential for exposures due to atmospheric transport and deposition of pesticides and related contaminants may pose risks to humans and wildlife. Emissions of chemicals to air are related to physicochemical properties (e.g., vapor pressure and chemical stability). Experimental design and computer-based modeling, as related to emissions and dispersion of pesticides along transects downwind from release sources, will be discussed using the example of pesticide volatilization and drift in California agriculture that results in the transport and deposition downwind to the Sierra Nevada mountains, where much work has been done to refine exposure data for use in risk assessment and management. Predictably, those chemicals found frequently in air are those used most extensively, have multiple emission sources, and resist degradation. Yet to be determined are definitive connections with adverse impacts to humans and wildlife, although the accumulating evidence suggests that endocrine disrupting chemicals, ChE inhibitors, and others warrant further attention. Steps that are being taken to limit emissions, such as in pest control and fuel combustion, offer promising opportunities for improving the quality of air and of the overall environment. Chemical degradation rates and products from trace organics in the air merit more attention, as do the potential for activation by photooxidation and bioaccumulation in food chains. The potential effect of climate change, on atmospheric processes affecting contaminant behavior, is an area ripe for further study.

Molecular Characterization of Nitrogen-Containing Organic Compounds in Humic-like Substances Emitted from Straw Residue Burning

The molecular composition of humic-like substances (HULIS) in different aerosol samples was analyzed using an ultrahigh-resolution mass spectrometer to investigate the influence of biomass burning on ambient aerosol composition. HULIS in background aerosols were characterized with numerous molecular formulas similar to biogenic secondary organic aerosols. The abundance of nitrogen-containing organic compounds (NOC), including nitrogen-containing bases (N-bases) and nitroaromatics, increased dramatically in ambient aerosols affected by crop residue burning in the farm field. The molecular distribution of N-bases in these samples exhibited similar patterns to those observed in smoke particles freshly emitted from lab-controlled burning of straw residues but were significantly different with those observed from wood burning. Signal intensity of the major N-bases correlated well with the atmospheric concentrations of potassium and levoglucosan. These N-bases can serve as molecular markers distinguishing HULIS from crop residue burning with from wood burning. More nitroaromatics were detected in ambient aerosols affected by straw burning than in fresh smoke aerosols, indicating that many of them are formed in secondary oxidation processes as smoke plumes evolve in the atmosphere. This study highlights the significant contribution of crop residue burning to atmospheric NOC. Further study is warranted to evaluate the roles of NOC on climate and human health.

Polychlorinated dibenzo-p-dioxins, dibenzofurans, and dioxin-like polychlorinated biphenyls in rice straw smoke and their origins in Japan

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) contained in the smoke generated from rice straw burning in post-harvest paddy fields in Japan were analyzed to determine their congener profiles. Both the apportionment of toxic equivalent (TEQ) by using indicative congeners and the comparison of the homolog profiles showed that the PCDDs/PCDFs/DL-PCBs present in the rice-straw smoke were greatly influenced by those present as impurities in pentachlorophenol (PCP) and chlornitrofen (CNP, 4-nitrophenyl-2,4,6-trichlorophenyl ether) formulations that had been widely used as herbicides in paddy fields in Japan. Further, in order to investigate the effects of paddy-field soil on the PCDDs/PCDFs/DL-PCBs present in rice-straw smoke, PCDD/PCDF/DL-PCB homolog profiles of rice straw, rice-straw smoke and paddy-field soil were compared. Rice-straw smoke was generated by burning rice straw on a stainless-steel tray in a laboratory. The results suggested that the herbicides-originated PCDDs/PCDFs/DL-PCBs and the atmospheric PCDDs/PCDFs/DL-PCBs contributed predominantly to the presence of PCDDs/PCDFs/DL-PCBs in the rice-straw smoke while the contribution of PCDDs/PCDFs/DL-PCBs formed during rice straw burning was relatively minimal. The major sources of the PCDDs/PCDFs/DL-PCBs found in the rice-straw smoke were attributed primarily to the paddy-field soil adhered to the rice straw surface and secondarily to the air taken by the rice straw. The principal component analysis supported these conclusions. It is concluded that rice straw burning at paddy fields acts as a driving force in the transfer of PCDDs/PCDFs/DL-PCBs from paddy-field soil to the atmosphere.

Strategies for the identification of non-polar toxicants in aqueous environmental samples using toxicity-based fractionation and gas chromatography-mass spectrometry

Toxicity-based fractionation is a useful tool for the isolation and identification of non-polar organic compounds that are present at toxic concentrations in aqueous environmental samples. Methods for isolating such toxicants from the aqueous sample matrix and techniques for fractionating the compounds for the purpose of reducing the complexity of the sample matrix and thus facilitating identification are evaluated. Strategies for analyzing gas chromatographic-mass spectrometric data and confirming toxicant identification are presented. Studies that use toxicity-based fractionation for identifying the cause of toxicity in aqueous environmental samples such as municipal and industrial wastewater treatment plant effluents and ambient waters are discussed.

Evaluation of the mutagenicity of combustion particles from several common biomass fuels in the Ames/Salmonella microsome test

We have evaluated the mutagenicity of dichloromethane extracts of combustion particles from several biomass fuels that are commonly used in developing countries in Salmonella strains TA98 +/- S9 and TA100 +/- S9. Combustion-particle extracts from dried cow dung and crop residue exhibited mutagenic potencies similar to wood-smoke extracts (0.0-1.0 rev./microgram extract). However, extracts from coconut-shell-smoke particles showed relatively potent direct-acting mutagenicity (1.6 rev./micrograms, TA98-S9). Results from testing this sample in nitroreductase- and acetylase- deficient strains TA98NR and TA98 (1,8-DNP-6) revealed no contribution from nitroarenes.